1. Field of the Invention
The present invention relates to a speed control system for a vehicle having a braking device and a stepless transmission, particularly a hydrostatic transmission.
2. Description of the Related Art
A working vehicle having a stepless transmission, e.g. an HST (hydrostatic transmission) as a change speed device includes a foot-operated change speed pedal for controlling the HST, and a shift lever for manually operating the change speed pedal, as disclosed in Japanese Patent Publication Kokai No. 1989-190553. Generally, such a vehicle also includes a lock mechanism for maintaining the shift lever in a selected position. The vehicle can run at a constant speed, i.e. make a cruising run, when the driver's foot is removed from the change speed pedal after operating the shift lever to set the change speed pedal to a selected forward speed position and retaining the shift lever in the corresponding position by means of the lock mechanism.
The retaining action of the lock mechanism is canceled when a brake pedal is depressed during the constant speed run as above. Then, the HST and shift lever are returned to neutral position by an urging spring acting on the HST, and the brakes are applied at the same time.
In the above speed control system, not only the HST but the shift lever returns to neutral when the brake pedal is depressed during a cruising run at the constant speed with the lock mechanism in operation. In order to resume the constant speed run after depressing the brake pedal, therefore, the driver must operate the shift lever back to the position corresponding to the constant speed.
The driver operates the shift lever to set a desired running speed while looking ahead. In this case, the driver does not correctly grasp the position to which the shift lever should be operated. It is therefore difficult to set the shift lever to the previous position correctly. To cope with this difficulty, the driver must confirm positions of the shift lever whenever the shift lever is operated. This operation, though temporarily, distracts the driver's attention from a forward view, which is undesirable for the purpose of driving.